ABO system

Definition

the main human blood group system used for matching blood for transfusion. it gives four blood groups A, B, AB and O) as a result of the presence or absence of either or both of two antigens (A or B) on the red blood cells and the presence of naturally occurring antibodies against the absent antigen(s) in the serum. This result agglutination of red blood cells and transfusion shock if blood is given to an individual of an incompatible blood group. Where the AB group possesses both A and B antigens and the O group possess none